This invention relates to a tool and method for capturing an object in a cavity, and more particularly, but not by way of limitation, relates to apparatus and method adapted for retrieving a packer from a subterranean borehole.
A sealing device, commonly referred to as a "packer" is often used in a subterranean borehole or well to seal off or plug a zone or zones of the borehole. It is often necessary to remove the packer from the borehole. This is typically accomplished using a rotary drill or rotary milling tool to "drill up" or "mill up" the packer. The milling tool or mill is normally lowered into the borehole on a drill string until it contacts the packer at which time it is rotated to mill away the outer edge of the packer, thereby freeing the packer from the borehole. This milling process leaves large pieces of the packer between the mill and the core of the packer. The pieces will fall into the borehole if the mill is lifted or moved relative to the packer in such a manner that the pieces are not contained by the mill.
If the debris from the milled packer is allowed to fall into the borehole during the milling operation, the debris may damage other tools and the like which are located below the packer in the well. The debris may also be blown out of the well at a later time and cause damage to the tools and the equipment located at the wellhead. It is therefore desirable to provide a means for containing the debris created by the milling operation. It is also desirable to provide a retrieving tool and method which operates simply and reliably with a minimal number of moving parts and which will capture and release the packer with minimal manipulation of the drill string and tool.
The prior art includes numerous apparatus for retrieving a packer and for catching the packer once it is freed from the borehole. This is particularly so of the "bridge plug"-type packer. Most of the prior art apparatus include a central stinger which is passed through a central bore of a packer and which includes a central mandrel with a sliding sleeve disposed thereon having resilient spring fingers. After passing downward through the packer, the sliding sleeve drops down to an enlarged diameter tapered surface of the mandrel causing expansion of the spring fingers so that they will not pass upwards through the packer bore.
One particular example of such a prior art retrieving tool is manufactured by Bowen Tools, Inc. and is illustrated in their Instruction Manual No. 5/2710 entitled "Bowen Simplex Packer Retrievers", 7th printing, dated June 1974.
The Bowen device is a rotary mill-type packer retrieving tool that consists of a washover-type mill shoe and a centrally located spear that passes through the packer mandrel bore. The spear or central mandrel has a cantilever finger collet sleeve with expanding fingers pointed in a downward direction. After the stinger passes through the packer bore, the collet sleeve drops down to an enlarged diameter tapered surface or wedge. This causes expansion of the sleeve fingers, thus causing the diameter increase which will not pass back through the packer bore, thereby creating a shoulder which catches the packer mandrel so that the packer may be retrieved. This expanded diameter also serves to catch the packer or bridge plug after milling away the outer slips that hold the packer in place with the borehole. The milled packer is then retrieved from the borehole.
Another example of a prior art retrieving tool is disclosed in U.S. Pat. No. 4,254,983, invented by Harris, and assigned to the present applicant (the Halliburton Company). The Harris patent reverses the orientation of the collet sleeve used by the Bowen device so that the spring fingers are extended upwardly. The outside diameter of the flexible collet sleeve fingers is larger than that of the inner bore of the packer through which the Harris retrieving tool is to be stabbed. Consequently, the initial stab-in of the retrieving tool stinger requires compressing the fingers to cause their diameter to contract by applying a downward force. The fingers then expand to their normal larger outside diameter after passing through the packer bore thus creating an interference or catcher shoulder with respect to the packer mandrel when retrieving tool is pulled upward.
Another retrieving tool is disclosed in U.S. Pat. No. 3,095,926, issued to Rush. In the Rush apparatus, the stinger or spear does not pass through the packer but uses a bowspring and slip mounted on a cage on the end of the spear. The spear must be lowered into the packer to move the cage to the upper end of the spear. The tool must be rotated to release the cage from the upper end of the spear and then lifted to pull a slip expander up into the cage, thereby expanding the slips to secure the spear inside the packer.
Shortcomings of the prior retrieving tools include their complexity, i.e., the use of a sliding cage, fingers, slips, etc. which increase cost and the number of components which may fail; and that the mill does not contain the loose pieces of the milled packer.
Therefore, there is a need for apparatus and method which provide a retrieving tool of simplified structure and which will contain loose pieces of a milled packer.